Method and apparatus for continuous welding of plastics sheets,in particular for use in the manufacture of exploratory balloons

ABSTRACT

1. A device for continuously ultrasonically welding together overlapping edges of very thin films of thermoplastic material, comprising a first operative component in the form of an anvil, a second operative component in the form of an ultrasonic welding head with a welding tool opposite and adjacent said anvil, said operative components being movable relative to each other towards and away from each other, means for guiding said edges in overlapping longitudinal relation between said operative components, yieldable clamping means responsive solely to gravity for continuously and flexibly urging one of said operative components towards the other with a constant force in order to uniformly and continuously clamp the overlapping edges between said operative components, means for continuously supplying power to said welding tool in order to weld together the clamped overlapping edges, an enclosure in which said power supply means is housed, means for circulating coolant liquid through said enclosure and over said power supply means immersed therein to keep the temperature of said tool constant, and drive means for continuously driving at uniform speed the welded overlapping edges longitudinally away from said operative components.

M. H. BOCQUET ETAL RATUS Oct. 15, 1974 $841,947

IETHOD AND APPA FOR CONTINUOUS WELDING O! PLASTICS SHEETS, IN PARTICULARFOR USE IN THE MANUFACTURE OF EXPLORATORY BALLOONS Original Filed Oct.22, 1969 2 Sheets-Sheet 1 M. PARAT SHEETS, IN PARTICULAR FOR USE IN THEHANU OF EXPLORATORY BALLOONS Original Fi1ed 0ct. 22, 1969 H. BOCQUETETAL 3,841,947 US FOR CONTINUOUS WELDING OF PLASfiICS FACTURE Oct. 15,1974 METHOD AND AP 2 Sheets-Shet 2' Claims priority, application France,Oct. 24, 1968,

Int. Cl. B32b31/08, 31/16 US. Cl. 156-580 6 Claims ABSTRACT OF THEDISCLOSURE A balloon made of a plurality of gores of film of plasticmaterial such as polyethylene terephthalate ultrasonically weldedtogether edge to edge to form an envelope with two polar apertures whichare then sealed by ultrasonically welding a pair of polar caps. Thesecond cap is conveniently welded through a hole provided in the firstcap to receive a valve for the balloon. Ultrasonic welding of the verythin film is made easier by inserting paper tapes between the tips ofwelding tool and anvil and the material being welded.

This is a continuation of Ser. No. 868,559, filed Oct. 22, 1969, nowabandoned. The invention relates to an improvement in or modification ofthe invention claimed and described in application Ser. No. 626,595, nowUS. Pat. No. 3,533,865, which is the parent of continuationin-partapplication Ser. No. 868,559.

In our above-mentioned patent Application, a method of a device foreffecting continuous ultrasonic welding has been described by means ofwhich it is possible in particlular to produce stratospheric balloonsfrom very thin sheets of plastic material such as polyethyleneterephtalate.

The method described in our above-mentioned patent Application, appliedto the manufacture of a balloon, an envelope or a similar object,consists in placing two sheets of material edge-to-edge with a smalldegree of overlap, and of soldering them together longitudinally usingultrasonic techniques, and of then shifting the assembly laterally inorder to proceed with the welding of another sheet along the edge ofsaid assembly, and so on until the final welding of the free edges ofthe first and last sheets. In order, more particularly, to manufacture aballoon, the sheets take the form of gores which are welded togetheralong lines which will ultimately be meridian lines of the balloon, theballoon being finished off by fitting two polar caps of the samematerial as the gores and welding these continuously by the sameultrasonic techniques, along parallels of the balloon in slight overlapwith the terminal edges of the welded gores.

In one embodiment described in our above-mentioned patent Application,after having welded the first cap in position, the second is also weldedin position using as the welding anvil an appropriate metal elementlocated inside the envelop, for example a balloon valve head.

In accordance with the present invention, the welding of the second capis effected through an opening formed in the first cap, which opening isdesigned to ultimately receive the balloon valve.

The welding device described in our above-mentional patent applicationcomprises a welding head the chief United States Patent M 3,841,947Patented Oct. 15, 1974 element of which is a tool (called an electrode)which is supplied with power from a magnetostrictive arrangement andcarries out the welding together of the strips of plastic materialstrapped between it and an anvil. The already welded gores of theballoon are placed upon a hemispherical support which is caused torotate and the edge of which is tangential to the anvil, whilst thesheet which is to be welded is supported by a table equipped with aguide arrangement for the edges of the sheets downstream of the weldinghead.

In a particular embodiment described in our abovementioned patentapplication, the anvil is fixed and the Welding head is movable by theaction of a double-acting ram, this making it possible to retract thetool from the anvil and also to move it into contcat therewith under aconstant and controllable pressure. The drive element is a rollercarried by an arm connected to the welding head through a spring. Thewelding tool has an aluminium tip. The cooling of this tool and of themagnetostrictive assembly is effected by means of an air circuit.

It has now been determined, in the course of trials, that the jack whichproduces vertical displacement of the welding head and forces the toolagainst the anvil, prevents this mobile assembly from properly followingthe small vertical displacements which it must carry out during welding,so that the pressure exerted by the tool undergoes slight variations.The quality of the weld is therefore not strictly uniform from one endto the other.

In accordance with a further feature of the present invention, thisdrawback is overcome by resorting to gravitational means to produce thewelding pressure between tool and anvil, and by parting the tool and theanvil from one another between the welding passes in order to enable thesheets being welded together to be manipulated by means of adouble-acting jack acting against the gravitational force.

Preferably, the welding head will be fixed in the translatory mode, thatis to say, so that it cannot move towards or away from the table;instead the anvil is movable to enable it to be applied against the toolby gravitational force and to be removed therefrom by the operation ofthe the double-acting ram. In one embodiment, the anvil is carried by arocker with an adjustable counterweight which forces it against thetool. The said counterweight acts on the rocker by contact in suchfashion that during a first phase, the anvil approaches the tool rapidlyand in a second phase more slowly; at the end of its travel, contact isbroken and the counterweight acts simply on the rocker in order toproduce the welding pressure.

In accordance with another feature of the invention, the driving of thewelded sheets or films downstream of the welding head is effected by tworollers in contact with opposite faces of the sheets, at least one ofwhich rollers is driven. The welding of balloons or sheaths requiresthat the bottom roller is not connected to the frame of the welding headby an arm which would be in the way. On the other hand, this bottomroller, which has to resist the pressure of the top roller required todrive the welded sheets, must not transmit this pressure to the anvilsince this would disturb the welding operation. Accordingly, the bottomroller is separated from the welding head and the anvil; it is carriedby a component which at least partially surrounds the anvil withoutbeing in contact therewith.

In accordance with another feature, the tool does not have a separatetip but is a one-piece component, preferably of stainless-steel ortitanium. That of its faces located opposite the anvil takes the form ofa convex slipper having curvature both in the direction of its ownlength, which is arranged along the line of the weld which is to beproduced, and in the direction of its own width, which is quite small(in the order of some few mm.),

the width dimension being disposed perpendicularly in relation to saidline of weld.

This kind of tool must be aligned in the direction of feed of the sheetsbeing welded. However, it may be necessary for reasons of size, toexecute welds in a direction other than that defined by the edge of thetable. The tool will then preferably be mounted to pivot about avertical axis, and the top drive roller of the weld sheets likewise.

A variant embodiment of the invention is one in which the assembly ofwelding head and roller is movable about a vertical axis.

Welding trials on large lengths of material have indicated that theuniformity of the weld can only be obtained if the tool maintainsconstant efiiciency during the whole of the operation and therefore doesnot become overheated. A simple air-cooling arrangement will not sufiicein this context. In accordance with a still further feature of theinvention, the temperature of the tool is kept strictly constant bymeans of a circulatory water system or system using some other coolingfluid of high specific heat.

The above improvements make it possible to operate the welding equipmentfor prolonged periods and yet continuously produce welds of goodquality. A device comprising these improvements can be used not only forthe manufacture of balloons, sheaths or envelopes, but also makes itpossible to carry out all kinds of continuous welds in particular theflat welding of strips of plastic material over very substantiallengths. In order to carry out the latter kind of operation, it ismerely necessary to replace the hemispherical rotating support used forballoons, by a simple table, the strips or bands which are being weldedtogether advantageously being routed over the tables in the conventionalway by conveyor belts or feed rollers.

It has not been possible hitherto eifectively to weld sheets of plasticmaterial smaller in thickness than about 251;. It has now beendiscovered, however, in the course of investigations, that it ispossible continuously to solder sheets much thinner than this byultrasonic techniques by placing, at either side of the sheets beingsoldered together, strips of a material which will not weld to saidsheets, for example, paper, one of said strips being in contact with theanvil and the other with the tool. This method also forms part of thepresent invention.

The description which follows with reference to the accompanyingdrawings will indicate by way of nonlimitative example how the inventionmay be carried into practice.

In the drawing: I

FIG. 1 illustrates a welding device in accordance with the invention,seen in section on the line II of FIGS. 2 and 3;

FIG. 2 is a sectional view on the line 11-11 of FIGS. 1 and 3;

FIG. 3 is a plan view of the device, the welding head being removed;

FIGS. 4 and 5 are fragmentary views which are respectively similar toFIGS. 1 and 2, showing the welding tool on a larger scale;

FIG. 6 is a schematic view illustrating the design of the weld of thesecond cap of a balloon;

FIG. 7 is a fragmentary view similar to that of FIG. 2, showing on alarger scale the welding of very thin sheets.

The device illustrated in FIGS. 1 to 3 is similar, broadly speaking, tothat described in our above-mentioned patent application. The rotatinghemispherical support 1, which is used chiefly for the manufacture ofballoons, is illustrated in broken line. The already welded part 2 ofthe balloon is placed over said support 1, whilst a sheet 3 yet to bewelded in position is placed on the table 4. The edges of said part 2and said sheet 3 are driven by rollers 5 and 6 located in convergentplanes in grooves 7a and 7b formed in a guide arrangement 7.

The slightly overlapping superimposed edges pass between an anvil 8 anda tool 9 which produces the weld, and the welded part is driven by meanswhich will be described hereinafter. The welding head is marked by thereference 10 and the reference 10a indicates the magnetostrictiveassembly.

The welding head 10 is fixed in height in relation to the table 4, i.e.it cannot move towaards or away from the same, however, it can berotated about the vertical axes XX of the tool 9 for a purpose whichwill be explained hereinafter. The anvil 8 moves in a slot 4a in thetable 4 and is carried by a side arm 11 pivoting about a horizontal axis12. The arm 11 contains slots 11a in which can engage a ring 13acarrying a counterweight 13 after the manner of a steel-yard. Thus, thewelding pressure, that is to say the pressure under which the sheets 1,2 are trapped between the anvil and the tool during welding, can beregulated by appropriately adjusting the mass of the counterweight 13and effecting an appropriate selection of the slots 11a in which thering 13a is engaged.

In order to part the anvil from the tool between welding passes, a valve14 is used to operate a pneumatic double-acting jack 15 in order thatthe end of its piston rod 15a lifts the arm 11 and causes it to pivot,raising the counterweight 13. If the jack 15 is then operated in theother direction, by means of the valve 14, the arm 11 will first of allpivot rapidly, and then more slowly, under the action of thecounterweight, in order to produce a rapid approach on the part of theanvil 8, followed by a phase of slower approach. At the end of itstravel, the piston rod 15a will be out of contact with the arm 11 andthus enables the counterweight to act alone to produce the weldingpressure.

The welded sheets are driven, downstream of the welding head 10, by apair of rollers 16, 17, in the form of wheels having rubber peripheriesbearing, opposite one another, on the top face of the sheet 3 and thebottom face of the sheet 2, respectively. The axle of the bottom wheel17 is fixed to a support 17a integral with the table 4 and its rimprojects through a slot 4b in said table. The axle of the top wheel 16is fixed to one end of a lever 18 articulated to an arm 19 fixed to theframe 10b of the welding head, the other end of which lever is urged bya spring 18a towards the arm 19. The wheel 16 is thus elastically urgedtowards the wheel 17. One of these two wheels is positively driven, thewheel 16 for example being driven by a flexible transmission as in themanner described in our above-mentioned patent application.

The temperature of the welding head 10 and tool 9 is maintained strictlyconstant by a circulatory water-cooling system the input of which ismarked 10c and the output 10a.

The tool 9 is illustrated in greater detail in FIGS. 4 and 5. It issubstantially wedge-shaped, its bottom face 9a forming a convex slippertwo or three mm. wide and six to eight mm. long, curved in bothlongitudinal and transverse directions as the drawing shows. The weldinghead 10 has a screwed stem 9b which screws into the tool 9 so that thelongitudinal axis of the slipper 9a is located in the plane of the wheel16.

In order to carry out welding of the gores of a balloon, the weldinghead 10 is placed in the position illustrated in FIGS. 1 and 2, i.e.with the longitudinal axis of the slipper 9a parallel to the edge 40 ofthe table 4 (FIG. 3), in which table the slot 4a is formed. This machinecan be used to carry out other kinds of welds, for example fiat weldingof strips of plastic material. For this purpose, all that is necessaryis to replace the hemispherical support 1 by a second table locatedagainst the edge 40 of the table 4, the whole of the rest of theequipment being used.

In order to carry out welds in a direction other than that of the edgeof the table, the assembly of frame 101),

welding head and supported arm 19, is rotated around the axis XX.

FIG. 6 illustrates the welding of the second cap 21 of a balloon 22,through an orifice 23a formed in the cap 23 already welded in positionin the manner described in our above-mentioned patent application. Thoseedges of the balloon and the cap 21 which are to be welded together, aretrapped between an anvil 8a and the tool 9, the latter passing throughthe orifice 23a. After the execution of the weld, in the conventionalway, the balloon valve is fixed in the orifice 23a. It would be withinthe scope of the present invention to trap the parts to be weldedtogether, between the tool 9 and an anvil, the former remaining outsidethe balloon and the latter passing through the orifice 23a. It wouldalso be possible, in the arrangement illustrated, to replace the anvil8aby an anvil rotating about an axis parallel to the axis XX of the toolbut offset in relation thereto in a manner described in ourabove-mentioned patent application in the context of the welding of thefirst cap.

FIG. 7 illustrates the welding of two very this sheets of plasticmaterial 24, 25. Two respective sheets of paper 26, 27 are placed uponthe top face of the sheet 4 and the bottom face of the sheet 5, alongthose of their edges which are to be welded together. Then, these edgesare arranged in such fashion that the top face of sheet 25 slightlyoverlaps the bottom face of the sheet 24 and the whole assembly ispassed between the anvil 8 and tool 9 in the manner already described.After the execution of the weld, the strips of paper 26 and 27 areremoved, these not being weldable to the sheets. The strips of paper canbe placed in the correct position before the sheet pass between anviland tool, or may be preliminarily fixed to the edges of the sheets whichare to be welded together by sticking them there. To this end, adhesivetapes can be used; the latter are particularly easy to remove from thesheets after welding.

It has proved possible, with this process, to effect continuousultrasonic welding of sheets of polyethylene terephthalate 9, inthickness, using strips 26, 27 of roneotype paper. However, it isobviously within the scope of the invention to replace the strips ofpaper by sheets of other materials which will not be ultrasonicallyWelded to the plastics material of which the basic sheets involved inthe construction are made.

What is claimed is:

1. A device for continuously ultrasonically welding together overlappingedges of very thin films of thermoplastic material, comprising a firstoperative component in the form of an anvil, a second operativecomponent in the form of an ultrasonic welding head with a welding toolopposite and adjacent said anvil, said operative components beingmovable relative to each other towards and away from each other, meansfor guiding said edges in overlapping longitudinal relation between saidoperative components, yieldable clamping means responsive solely togravity for continuously and flexibly urging one of said operativecomponents towards the other with a constant force in order to uniformlyand continuously clamp the overlapping edges between said operativecomponents, means for continuously supplying power to said welding toolin order to weld together the clamped overlapping edges, an enclosure inwhich said power supply means is housed, means for circulating coolantliquid through said enclosure and over said power supply means immersedtherein to keep the temperature of said tool constant, and drive meansfor continuously driving at uniforrn speed the welded overlapping edgeslongitudinally away from said operative components.

2. A device according to claim 1, wherein said gravity responsiveyieldable clamping means is adjustable to modify the magnitude of saidconstant force.

3. A device according to claim 2, wherein said yieldable clamping meanscomprises means for gravitationally pivoting one of said operativecomponents relative to the other about a fulcrum, said gravitationalpivoting means including an adjustably Weighted lever pivoted on saidfulcrum and bearing said one operative component.

4. A device according to claim 3, wherein said weighted lever comprisesan adjustably positionable weight acting as a counterweight with respectto said one operative component.

5. A device according to claim 4, wherein said one operative componentis said first component in the form of an anvil, whereas said secondoperative component in the form of a welding head is stationary.

6. A device according to claim 1, wherein said first operative componentin the form of an anvil is movable whereas said second operativecomponent in the form of an ultrasonic welding head is stationary,wherein said power supply means and said coolant liquid circulatingfiealns are integral portions of said stationary welding ReferencesCited UNITED STATES PATENTS 3,438,428 4/1969 Balamuth et a1 156733,445,307 5/1969 Balamuth et a1. 15673 3,657,802 4/1972 Delrnas 156733,388,848 6/1968 Youmans et al. 228-1 3,492,847 2/ 1970 Ustyantsev eta1. 228 1 3,193,169 7/1965 Arnold 15673 DANIEL J. FR'ITSCH, PrimaryExaminer US. Cl. X.R. 15673

1. A device for continuously ultrasonically welding together overlappingedges of very thin films of thermoplastic material, comprising a firstoperative component in the form of an anvil, a second operativecomponent in the form of an ultrasonic welding head with a welding toolopposite and adjacent said anvil, said operative components beingmovable relative to each other towards and away from each other, meansfor guiding said edges in overlapping longitudinal relation between saidoperative components, yieldable clamping means responsive solely togravity for continuously and flexibly urging one of said operativecomponents towards the other with a constant force in order to uniformlyand continuously clamp the overlapping edges between said operativecomponents, means for continuously supplying power to said welding toolin order to weld together the clamped overlapping edges, an enclosure inwhich said power supply means is housed, means for circulating coolantliquid through said enclosure and over said power supply means immersedtherein to keep the temperature of said tool constant, and drive meansfor continuously driving at uniform speed the welded overlapping edgeslongitudinally away from said operative components.